1. Field of the Invention
The present invention relates to a charging device for cameras and, more particularly, to a charging device for cameras which is used for a charging apparatus usable as a driving source for various operations within a camera and which executes the charging operation by means of an actuator made of a shape memory alloy.
2. Description of the Prior Art
Various charging apparatuses for driving a shutter, a lens barrel and the like are provided within a camera. For example, a charging apparatus for a shutter is charged with a spring urging force, which is a driving force for the shutter, by a driving force from a DC motor or the like which is used for the purpose of feeding a film in coupling with the film taking-up operation.
FIGS. 4(a) and 4(b) show a conventional spring urging force charging apparatus of a program shutter for adjusting exposure by, for example, two blades provided on the back side of the shutter portion. In FIG. 4a, when the film is taken up after photographing is finished, for example, a sliding plate 10 is pressed by a cam or the like in the direction indicated by the arrow 100 so as to slide on a shutter plate 2. At the point where a driving lever 8 is engaged with a shutter lever 6, a catch 13 is locked in an engaging groove 10a. At this time, the driving force of the shutter is charged by a driving spring 12.
When a shutter release button is pressed, an electromagnet 16 is turned on, thereby holding a closing lever 14. Since the catch 13 is released when the shutter release button is pressed, the sliding plate 10 slides downward. As a result, the driving lever 8 presses down the shutter lever 6 (pushes up a pin 6a) and opens shutter blades 1a, 1b. As shown in FIG. 4b, the two shutter blades 1a and 1b rotate around pins 4a and 4b, respectively, of a presser plate 3 as their axes so as to open a shutter aperture 2a.
At this time, a light quantity sensor (not shown) detects the exposure and when the exposure reaches a predetermined value, the electromagnet 16 is turned off, so that the closing lever 14 which is out of contact with the electromagnet 16 rotates by virtue of the urging force of a spring 15, and a closing pin 14a presses a cam portion 8b of the driving lever 8, thereby releasing the engagement between a holding claw 8a and a projection 6c. The two shutter blades 1a, 1b are closed by virtue of the urging force of a spring 7, thereby finishing the shuttering operation.
In the conventional charging apparatus shown in FIG. 4, however, the driving force of the DC motor for taking up a film is transmitted to the sliding plate through a gear train, a cam and the like, and the spring force is charged by the sliding operation of the sliding plate. The charging apparatus is therefore complicated and requires a considerable space. Thus, a conventional charging apparatus is a barrier to the reduction in weight and size of a camera.
In addition, since the release of the charging apparatus is carried out by the operation of the electromagnet 16 and the catch 13 which is started by the operation of pressing down the release button, the apparatus is complicated. Furthermore, since the operation of the electromagnet 16 produces a sound, quiet operation is impossible.
In photographing, it is often required to take a picture of an animal in the natural world, a child or the like in the natural state thereof. It is therefore expected to produce a silent-operation camera which enables photographing free from a sound produced by an operation such as shuttering.